Beat egg whites until they reach the soft peak stage. While stirring slowly add sugar, vanillin and yolks. Add mascarpone and keep stirring until you get a soft cream without clots. In a bowl stir coffee, liqueur and sugar. Dip one buiscuit at the time and layer them on a cooking dish or pan. Divide the cream into two and pour one half on the fisrt biscuit layer. Prepare a second layer of biscuits on top, in the same way. Add cocoa to the second half of cream and stir it into a uniform brown cream. Pour the cream on top. Sift a thin layer of cocoa on top of the tirami su and chill for a couple of hours before serving. If you happen find out you need some more biscuits or liquid mix don't worry, just add more ingredients.